XPS M1710 Graphics Card Upgrade

Hello forum!

                     I have a Dell XPS M1710 fitted with a Geforce Go 7900GS with 256 MB. I was looking to upgrade the card but I think the biggest I can put in is the Geforce Go 7950 GTX with 512 MB. I have heard that this card has a few problems with heat, but I have a friend who has the same model and he plays games with a large room fan blowing on the back of the laptop and it runs fine. What I need to know is if the upgrade would be worth it, how easy would it be to fit (I like to think that I am at an Intermediate level of computer maintenance) and where could I look to buy one in the UK? Thanks for any help that anybody can give me.

Ed.